private void SetBitmap(Bitmap bitmap, byte opacity)
{
if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
throw new ApplicationException("The bitmap must be 32ppp with alpha-channel.");
IntPtr screenDc = WinApi.GetDC(IntPtr.Zero);
IntPtr memDc = WinApi.CreateCompatibleDC(screenDc);
IntPtr hBitmap = IntPtr.Zero;
IntPtr oldBitmap = IntPtr.Zero;
try
{
hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
oldBitmap = WinApi.SelectObject(memDc, hBitmap);
WinApi.SIZE size = new WinApi.SIZE(bitmap.Width, bitmap.Height);
WinApi.POINT pointSource = new WinApi.POINT(0, 0);
WinApi.POINT topPos = new WinApi.POINT(Left, Top);
WinApi.BLENDFUNCTION blend = new WinApi.BLENDFUNCTION
{
BlendOp = WinApi.AC_SRC_OVER,
BlendFlags = 0,
SourceConstantAlpha = opacity,
AlphaFormat = WinApi.AC_SRC_ALPHA
};
WinApi.UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, WinApi.ULW_ALPHA);
}
finally
{
WinApi.ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
WinApi.SelectObject(memDc, oldBitmap);
WinApi.DeleteObject(hBitmap);
}
WinApi.DeleteDC(memDc);
}
}
public static extern WinApi.Bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref WinApi.POINT pptDst, ref WinApi.SIZE psize, IntPtr hdcSrc, ref WinApi.POINT pprSrc, int crKey, ref WinApi.BLENDFUNCTION pblend, int dwFlags);